iconv_strlen

Description

In contrast to strlen(),
iconv_strlen() counts the occurrences of characters
in the given byte sequence str on the basis of
the specified character set, the result of which is not necessarily
identical to the length of the string in byte.

As such it is being "stricter" than mb_strlen and it may mean you need to check for invalid sequences first. A quick way to check is to exploit the behaviour of the PCRE extension (see notes on pattern modifiers);